1. Field of the Disclosure
The present disclosure relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device having a nano pattern for improving the optical efficiency and a method of manufacturing the same.
2. Description of the Related Art
A light emitting diode (LED) is a device used for emitting signals converted from electric energy to light such as an infrared ray or visible ray using the characteristics of a compound semiconductor. The LED is a type of electroluminescent (EL) device, and these days, Group III-V compound semiconductor LEDs are largely utilized.
A Group III nitride compound semiconductor is a direct transition type semiconductor that can operate stably at higher temperatures than devices using other types of semiconductors, and is used widely in light emitting devices such as LEDs or laser diodes (LDs). Such Group III nitride compound semiconductors are usually formed on a sapphire (Al2O3) substrate. Research is being conducted on various types of LEDs in order to increase the light emitting efficiency, that is, the optical output efficiency. For example, research is being conducted on forming an uneven structure in an optical output region of a LED to increase the optical output efficiency.
At interfaces of material layers having different refractive indices, optical propagation is limited according to the refractive index of each material layer. When light proceeds from a semiconductor layer having a great refractive index n=2.5 to an air layer having a small refractive index n=1 on a planar interface, light should be incident on the planar interface at a predetermined angle or smaller with respect to a vertical direction of the interface. When light is incident at a predetermined angle or greater, light is totally internally reflected on the planar interface and the optical output efficiency is greatly decreased. Thus, in order to prevent this decrease in the optical output efficiency, attempts have been tried to introduce an uneven structure at the interface.
FIG. 1 is a schematic view illustrating a conventional semiconductor light emitting device including an uneven structure.
Referring to FIG. 1, an n-GaN layer 112 is formed on a sapphire substrate 111, and an n-AlGaN layer 113, an active layer 114, a p-AlGaN layer 115, a p-GaN layer 116, and a p-electrode 117 are sequentially formed on a portion of the n-GaN layer 112. Then an n-electrode 118 is formed in a portion of the n-GaN layer 112 where the n-AlGaN layer 113 is not formed. The above-described structure outputs light generated in the active layer 114 in a flip-chip form mainly to the transmissive sapphire substrate 111. An uneven structure 120 is formed on the surface of the sapphire substrate 111 to increase the optical output efficiency. The uneven structure 120 is used for increasing the optical output efficiency. However, when the sapphire substrate 111 is patterned to form the uneven structure 120, particularly as illustrated in FIG. 1, the crystal structure of the sapphire substrate 111 and the semiconductor layer formed on the sapphire substrate 111 do not match each other and thus defects are likely to be generated in the semiconductor layer. Thus it is difficult to grow a uniform semiconductor layer. Accordingly, the optical efficiency is decreased due to inner crystal defects.